This invention relates to grain storage bins, and more particularly to sweep augers for unloading grain from such storage bins.
"Sweep augers", which are the subject of this invention, are used to unload grain from grain storage bins which are of upright, generally cylindrical construction. These grain storage bins have a floor with a central discharge opening. All grain which is stored in the bin is removed from the bin through the discharge opening.
Grain bins of this kind generally use a horizontal "unloading auger" (which is different from a "sweep auger") to move the grain from the opening in the bin floor to a point outside the bin. Generally, the unloading auger is located under the bin floor, leaving the floor in the bin clear of any obstructions. The unloading auger is commonly mounted in a horizontal discharge pipe or sleeve. The inner end of the sleeve communicates with the discharge opening, and discharged grain is collected outside the bin when moved through the sleeve by rotating the unloading auger. Grain is removed from the bin by the unloading auger until all the grain that will flow naturally from the bin through the discharge opening is gone. The top surface of the grain remaining in the bin extends upwardly at an angle of about 30.degree. to 35.degree. (called the angle of repose) from the center opening in the bin floor to the bin wall in all directions from the center. In a large diameter storage bin the grain remaining is considerable and can represent thousands of bushels. The purpose of a sweep auger is to bring this remaining grain to the center opening of the bin where it can be removed by the unloading auger.
In some types of sweep auger drive units, the inner end of the auger is attached to a motor and drive unit located in the center discharge opening of the bin. The sweep auger is placed in the bin and connected to the drive unit after the initial grain has been removed to expose the center opening. In other types of sweep auger drive units, a motor for driving both the unloading auger and the sweep auger is located outside the bin. A power transfer unit in the central opening of the bin floor is connected to the unloading auger and to the sweep auger. The motor outside the bin provides the power for the sweep auger. The sweep auger is left in the bin at all times, rather than being connected to the drive unit only after the initial grain has been removed. The sweep auger is started by a clutch mechanism after all grain that will flow naturally has been removed by the unloading auger. In either drive unit, the sweep auger extends radially from the vicinity of the central discharge opening toward the bin wall and is slightly shorter in length than the bin radius.
The sweep auger is ordinarily used in combination with a long shield which extends parallel to and alongside the auger. Augers used with a shield have certain advantages, but many times a sweep auger is used without a shield. In either instance, the attachment between the sweep auger and the drive unit allows the sweep auger to rotate about its axis and also permits angular travel of the auger around the interior of the storage bin.
When the sweep auger is used without a shield, the auger rests on the grain surface as it rotates to pull the grain toward the center opening. As the auger rotates it travels through several revolutions around the bin and lowers the grain level uniformly throughout the bin. Usually there is a wheel on the bin wall end of the sweep auger which is slightly larger in diameter than the auger. The wheel contacts the bin floor when the auger finally reaches the vicinity of the floor to prevent the auger from scratching directly on the floor.
The more common sweep auger is equipped with a shield. The shield extends the full length of the auger, and is mounted on the side of the auger remote from the direction of travel of the auger around the bin. The height of the shield is usually about equal to the diameter of the sweep auger. The surface of the shield facing the auger is somewhat concave so as to conform to the round shape of the auger and is located about one inch from the auger. When the sweep auger and shield are placed in a bin they initially rest on the grain surface. When the sweep auger is rotated it will throw grain against the shield in the process of pulling grain toward the bin center. This causes the shield to hold back the auger and prevents it from traveling around the bin as does the sweep auger without a shield. As a result, the auger digs down into the pile of grain, following a downward path of about a 45.degree. angle, until it reaches the vicinity of the floor. From that point on it continues to advance into the grain pile around the floor and empties the bin in one revolution of the sweep auger around the bin. The forward propulsion of the sweep auger comes from a wheel mounted on the bin wall end of the auger shaft. The wheel is usually about 1 inch to 11/2 inches larger in diameter than the sweep auger. The contact of the spinning rubber wheel against the bin floor provides the forward travel of the sweep auger.
One advantage of using a shield is that it leaves the bin floor cleaner as it continually scrapes up grain thrown against it by the auger. The lower the shield can be adjusted to the floor, the better the cleaning job that will result. However, if the shield adjustment is too low, or if the shield or auger sags mid-span under its own weight, the forward travel of the auger will be stopped because of excessive drag on the bin floor. This latter problem is a serious one when a shield is not very resistant to torque.
Grain storage bins vary in diameters from about 15 to 60 feet, but in recent years larger storage bins having diameters of 75 feet and larger have been used. In most bins, but especially the larger diameter bins, the sweep auger tends to sag mid-span under its own weight. In units where a shield is used, the shield also tends to be flexible longitudinally and sags in the center. Moreover, shields are not strong torsionally and have a great tendency to twist about their longitudinal axes.
In the past, some shields have been reinforced by welding an elongated angle-iron to the shield to form a triangular cross-sectional structure having fairly good resistance to torsion. However, the present invention provides an improved sweep auger assembly having more stiffness longitudinally and torsionally than the prior art triangular structure, as well as an easier means for adjusting the height of the shield above the floor of the grain bin.